1. Field of the Invention
This invention relates to scraper blades for moving belts and, more particularly, to pivoting scraper blade assemblies which may be biased into engagement and biased out of engagement with the moving belt.
2. Description of Prior Art
Devices for separating solids from liquids, such as belt filter presses and gravity belt sludge thickeners, utilize moving belts. Belt filter presses use a series of cylindrical rollers about which a pair of belts is wrapped in a serpentine path. As the belts pass around each successive roller, liquid is pressed out of a material that is previously introduced between the belts while the solid matter remains trapped inside. Gravity belt sludge thickeners operate in a similar manner but separate the water from the solid mass from the effects of gravity only. These presses and thickeners typically use scraper blades at the discharge point of their process in order to scrape off any dewatered material that may have been pressed into or otherwise stuck to the weave of the belts. Scraper blades may also be positioned at other locations separate from the discharge point to aid in cleaning.
Scraper blade assemblies are necessary to insure that the solid material does not become reintroduced into the closed loop system of the press, which can be detrimental to both the performance and life of the press. At the same time, the scraper blade assemblies must allow some "give" for the seams of the belt, as well as allowing movement of the scraper blade away from the belt for cleaning and maintenance purposes.
Present scraper blade assemblies in use on belt filter presses and gravity belt sludge thickeners include a combination of springs, cams, rollers and brackets in order to engage or disengage the blade from the belt. These are complex and costly arrangements that limit the utility and flexibility of the scraper blade assembly. In addition, for very-wide machines, these arrangements often do not provide sufficient force for the scraper blade to work effectively when held against the belt.
U.S. Pat. No. 3,722,684 to Maestrelli discloses equipment for pre-filtering a solvent, particularly in dry-cleaning machines, wherein a scraper blade is kept under the action of a counterweight or spring in engagement with the outer cylindrical wall of a rotating drum. The adhesion or friction pressure of the blade against the drum is adjustable by adjustment of the spring force or the counterweight load.
U.S. Pat. No. 5,133,863 to Zander discloses a stripping device for rotary filters wherein a scraper blade scrapes filter cake from a belt. The scraper blade is carried on a cross bar, which in turn carries a weight. The weight may be adjusted to adjust the force of the scraper blade acting on the belt filter cake. A tilting device is arranged between the cross bar and the weight. A tie bar functions as a safety device against overthrow so that the tilting device is not overthrown when under too great a load. The center of gravity of the weight must always be between a transverse shaft and a belt if the scraper is to be engaged on the belt. The tilting device will tilt out of engagement with the belt when a temporarily large load on the scraper blade arises.
U.S. Pat. No. 4,154,686 to Ootani et al. discloses an apparatus for continuous liquid-solid separation having pivoting side plates which hold filter cloth on the device. The side plates are connected to a movable lever via a spring. When the lever is pushed outward, the spring causes the pivoting side plates to disengage from the filter cloth.
There remains a need for a scraper blade assembly for devices for removing liquids from solids which eliminates cams, brackets and levers and replaces them with a simplified singular arrangement for both engaging and disengaging the scraper blade. Furthermore, there is a need for a scraper blade assembly which may employ springs on either end of the scraper blade to resist torsional deformation which material being separated from the belt may impose on the scraper blade. There is also a need for a scraper blade which may be securely disengaged from the belt a greater distance from the belt than prior art arrangements, to facilitate cleaning and maintenance of the scraper blade assembly and the belt. There is also a need for a scraper blade assembly which provides a standardized design for various belt filter press and gravity belt sludge thickener machines.